There are several ways to supply the image for a toolbar button, including direct specification of an image object. The simplest approach is to use a symbol which is registered as an image identifier, including the pre-registered standard images, as in the preceding examples. For details of this and the other way to supply images, see toolbar-button.
You can, if desired, supply an alternative image which is displayed while the button is selected in a
:multiple-selection component (see Advanced toolbar features), using the initarg
In a toolbar-component it is possible to specify images for the buttons by supplying an image-set as the default-image-set , along with integers in the images initarg specifying the index for the image of each button:
CAPI User Guide and Reference Manual (Unix version) - 25 Feb 2015